To repair a tooth damaged by dental caries or by accident, a crown repair material such as a composite resin, metal, ceramic or the like is bonded to the tooth by an adhesive. As the adhesive for bonding a crown repair material to the tooth, there are currently available optically polymerizable adhesives and chemically polymerizable adhesives which are used depending on the type of a crown material. For example, an optically curable bonding material is used for repairing by using optically curable composite resins, while a resin cement which is a chemically polymerizable adhesive is used for repairing by using metal casts and ceramics.
The adhesive is required to keep the crown repair material firmly bonded to the tooth for a long time in such a severe environment as the oral cavity. If the adhesive strength of the adhesive is low or the durability of the adhesive is insufficient, the repair material may fall off, or a gap may be produced between the tooth and the repair material with the result that bacteria may enter the gap, causing secondary dental caries.
The hard tissue of a tooth consists of enamel and dentin and a crown repair material is required to be bonded to both enamel and dentin clinically. Heretofore, to improve adhesion, the surface of a tooth has been pretreated prior to the application of an adhesive. A material for this pretreatment is generally an acidic aqueous solution for demineralizing the surface of a tooth, such as an aqueous solution of phosphoric acid, maleic acid or citric acid. In the case of enamel, the adhesion mechanism to the treated surface is mechanical macroscopic retention produced when an adhesive permeates the surface that has been made rough by demineralizing with an acidic aqueous solution, and hardens. Thereby, sufficient adhesive strength is obtained clinically. On the other hand, in the case of dentin, the adhesion mechanism is mechanical microscopic retention produced when an adhesive infiltrates into micro voids of a sponge-like collagen fiber exposed to the surface of a tooth after demineralizing, and hardens. However, since the infiltration of the adhesive into the exposed collagen layer is not easy, a generally called primer which is a permeation accelerating material is used and hence, operation becomes complicated.
To cope with this problem, for the purpose of simplifying bonding operation, a primer for the simultaneous pretreatment of both enamel and dentin has been studied. Japanese Laid-open Patent Publication Hei 3-240712 discloses a primer composition comprising a polymerizable monomer containing an acidic group, a polymerizable monomer containing a hydroxyl group, water and a curing material; Japanese Laid-open Patent Publication Hei 4-8368 a primer composition comprising a polymerizable monomer containing an acidic group, a polymerizable monomer containing a hydroxyl group, water and an amino compound having an acid group; Japanese Laid-open Patent Publication Hei 6-192029 discloses a pretreatment material comprising vinyl phosphonic acid, vinyl phosphonic acid metal salt, carboxylic acid having a hydrophobic group, water and alcohol; Japanese Laid-open Patent Publication Hei 6-192030 a pretreatment material comprising an organic sulfonic acid metal salt, organic carboxylic acid having a hydrophobic group, water and alcohol; Japanese Laid-open Patent Publication Hei 7-82115 a primer composition comprising a vinyl compound having an acidic group, a vinyl compound having a hydroxyl group, water, aromatic sulfinic acid and amine; Japanese Laid-open Patent Publication Hei 7-89820 a primer composition comprising a polymerizable monomer having an acidic group, water and a compound having an amide group and a hydroxyl group in the molecule; and Japanese Laid-open Patent Publication Hei 7-97306 a primer comprising a polymerizable monomer having an acidic group, an organic solvent and water as well as an adhesive system in which a curable composition comprising a polymerizable monomer having an acidic group, a polymerizable monomer having a hydroxyl group and a polymerization initiator are used.
However, when an optically curable adhesive such as a bonding material for composite resins or the like is used, all of the above compositions have adhesive force to both enamel and dentin. However, when a chemically polymerizable adhesive such as resin cement or the like is used, the compositions cannot necessarily have sufficient adhesive force yet. Chemically polymerizable adhesives generally have a lower rate of polymerization than optically polymerizable adhesives and hence, are inferior in adhesive strength. When trialkyl boron (or partial oxide thereof) which has high catalytic activity among the chemically polymerizable adhesives is used, high adhesive strength can be obtained, but it is necessary to separately keep the catalyst from a polymerizable compound before use because the catalyst is chemically unstable. Or rather, therefore, it involves a drawback that operation becomes complicated.
To cope with this problem, not only when an optically polymerizable adhesive is used but also when a chemically polymerizable adhesive is used, the development of a pretreatment material which can gain excellent adhesive strength has been desired.